Condensed Matter Physics Seminar
2006/2007 | 2007/2008 | 2008/2009 | 2009/2010 | 2010/2011 | 2011/2012 | 2012/2013 | 2013/2014 | 2014/2015 | 2015/2016 | 2016/2017 | 2017/2018 | 2018/2019 | 2019/2020 | 2020/2021 | 2021/2022 | 2022/2023 | 2023/2024 | 2024/2025
2017-06-02 (Friday)
room 1.02, Pasteura 5 at 12:15 
Maria Ekiel-Jeżewska (IPPT PAN)Dynamics of flexible fibers in shear flow
In the literature, the typical suggested pattern of a single flexible fiber's evolution has been based on the concept of consecutive threshold values of the characteristic ratio A of bending forces to hydrodynamic forces (proportional to shear rate of the external flow), related to activation of consecutive characteristic fiber shapes or their sequences.In our joint work with A. Słowicka and H. A. Stone, we demonstrate that for the same value of A, different modes of the dynamics, which correspond to different characteristic shapes, can be observed, depending on the initial fiber configuration or orientation. Moreover, we show examples of fiber evolution with very long characteristic timescales,and with a long-lasting transient quasi-periodic mode which later changes into a different mode, with another shapesequence. Different modes can be observed consecutively during simulation of the same fiber.
2017-05-19 (Friday)
room 1.02, Pasteura 5 at 12:15
Krzysztof Wohlfeld (IFT UW)Hidden Magnetism and Correlations in the Spectral Properties of the Doped Mott Insulators
We study the evolution of the spectral properties upon hole or electron doping the Mott insulating state [1]. The spectral function of the Hubbard and t-J-like models is calculated using the cluster perturbation theory. We find that the features associated with the spin polaron and the 3-site terms dispersion, which dominate the Mott insulating spectrum [2], persist up to ca. 25% (40%) hole (electron) doping. We identify a quasi-free dispersion relation which crosses the Fermi level, develops at an almost infinitesimally small hole or electron doping, and evolves to a dispersion relation that is almost indistinguishable from the one given by the tight-binding model at the high doping level. Although naively such a quasi-free dispersion seems to be closely related to the free electronic hopping, our main result is that both the electron-electron correlations as well as the spin exchange interactions inherently influence this spectral feature. An intuitive explanation of this phenomenon is discussed and it is suggested that the “pseudogaps” can easily occur in such doped Mott insulators.[1] Y. Wang et al., unpublished (2017).[2] Y. Wang et al., Phys. Rev. B 92, 075119 (2015).
2017-05-05 (Friday)
room 1.02, Pasteura 5 at 12:15
Jacek Dziarmaga (IFT UW)Dynamics of quantum phase transitions: Kibble-Zurek scaling hypothesis
A system driven adiabatically across a quantum phase transition becomes excited near the quantum critical point according to a quantum version of the Kibble-Zurek mechanism. Its excited state satisfies a scaling hypothesis with a characteristiclength-scale and a time-scale that both depend on the transition rate and diverge in the adiabatic limit. This hypothesis was verified by an analytic solution of the quantum Ising chain, numerical simulations of the Bose-Hubbard model, and experiments with ultracold atoms.'
2017-04-28 (Friday)
room 1.02, Pasteura 5 at 12:15
Miłosz Panfil (IFT WF UW)Integrable models and condensed matter: alcoholic evenings, dynamic structure factors and quantum cooking
This talk will be a review some of our results on dynamical correlation functions of quantum integrable models. Focus will be placed on the experimentally relevant Lieb-Liniger model: a 1d model of interacting bosons. I will show how the correlations functions can be evaluated and how these predictions were tested experimentally with the Bragg scattering of cold atoms. On the more theoretical side I will discuss relations with a glorified conformal theory picture of the Lieb-Liniger model, namely the Luttinger liquid and present results on the dynamic structure factor at small momenta. We will finish with an inverse quantum cooking method.
2017-04-07 (Friday)
room 1.02, Pasteura 5 at 12:15
Alina Ciach (IChF PAN)Comparison of the amphiphilic and the colloidal self-assembly
In the first part of the talk amphiphilic systems are compared with systems containing sphericalparticles attracting each other at small-, and repelling each other at large distances (SALRinteractions). We show that close similarity between phase diagrams in these systems followsfrom the fact that both of them can be described by the Landau-Brazovskii (LB) functional. Keysteps of the coarse-graining procedure applied to the SALR system and leading to the LBfunctional are presented.In the second part of the talk exact results for one-dimensional (1D) versions of the SALRmodel and a model for lipids in water are compared. We show that the self-assembly leads tonumerous anomalies (such as increasing pressure for decreasing temperature at fixed density)that are associated with structural reorganizations that occur in response to changes of thethermodynamic state. The phase diagram of the SALR model in 2D will be presented if timeallows.
2017-03-31 (Friday)
room 1.02, Pasteura 5 at 12:15
Giacomo Gori (SISSA, Trieste)Percolation studies: charting old territory in statistical mechanics
2017-03-24 (Friday)
room 1.02, Pasteura 5 at 12:15
Konrad J. Kapcia (IF PAN)Charge order and metal-insulator transitions in the extended Hubbard model
Various charge-ordered states are relevant to a broad range of materials, e.g. manganites, cuprates, magnetite, doped transition metal compounds (Ti4xVxO7, WO3−x), heavy-fermion systems and organic compounds. The extended Hubbard model is one of the simplest models that captures the interplay between strong correlations and charge-ordering effects. The model can describe the insulator-metal transition between phases with long-range charge-order. We present studies of the model with both (i) on-site interaction U and (ii) intersite density-density interactions between nearest-neighbors W1 and next-nearest-neighbors W2 beyond the standard Hartree-Fock mean-field two-sublattice assumption. Using the dynamical mean-field theory we derived the ground state phase diagram of this model for arbitrary doping. The interplay between local and non-local interactions drives a variety of phase transitions connecting two distinct charge-ordered insulators (i.e., half-filled and quarter-filled), a charge-ordered metal and a Mott insulating phase. We investigate these transitions and the relative stability of the solutions and we show that the two interactions conspire to stabilize the quarter-filled charge-ordered phase. Additionally, we investigate the effects of next-nearest neighbor interactions on phase diagrams of the model in different limits and we show that charge-stripes can occur for repulsive W2>0 for both signs of W1.
2017-01-27 (Friday)
room 1.02, Pasteura 5 at 12:15
Jiri Chaloupka (Brno, Czech Republic)Soft spins and Higgs mode in Ca2RuO4
Mott insulators containing d4 ions with strong spin-orbit coupling may host anunusual "soft" magnetism due to a mixing of a nonmagnetic J=0 ionicgroundstate and low-lying magnetic J=1 levels. A competition of the exchange and spin-orbit couplings results in a quantum critical point (QCP) between nonmagnetic Mott insulator and magnetic order. Since the magnetic order is due to a condensation of the virtual J=1 levels and hence "soft", the amplitude (Higgs) mode is expected. We will discuss the recent neutron scattering and Raman scattering experiments demonstrating that this scenario applies to Ca2RuO4 containing Ru4+ d4 ions and directly probing the amplitude mode.
2016-12-16 (Friday)
room 1.02, Pasteura 5 at 12:15
Alina Ciach (IChF PAN)Effect of ions on thermodynamic Casimir potential
2016-12-09 (Friday)
room 1.02, Pasteura 5 at 12:15
Adam Rycerz (UJ, Kraków)